Search Results

The present study experimentally investigated the performance and emission characteristics of the diesel engine with hydrogen added to the intake air at late diesel-fuel injection timings. The diesel-fuel injection timing and the hydrogen fraction in the intake mixture were varied while the gross heating value per second of diesel fuel and hydrogen was kept constant at a certain value. NO showed minimum at specific hydrogen fraction. The maximum rate of incylinder pressure rise also showed minimum at 10 vol% hydrogen fraction. The indicated thermal efficiency was almost constant or slightly increased with small amount of hydrogen. A combination of hydrogen addition and late diesel-fuel injection timing contributed to low temperature combustion, in which NO decreased without the increase in unburned fuel.

Combustion simulation is an effective tool in overcoming the issues associated with gasoline HCCI engines, controlling ignition timing and extending the operating range. The research discussed in this paper commenced by optimizing the reaction mechanism from the perspective of ignition delay using the genetic algorithm (GA) method. Simulations employing the optimized reaction mechanism were then able to more accurately reproduce the ignition timing of iso-octane and primary reference fuels (PRF). Ignition times obtained from simulations showed excellent correlation with ignition times measured using these fuels in shock tube experiments, and in engines with both homogeneous and non-homogeneous fuel distributions. The use of the PRF mechanism for gasoline with an equivalent octane number enables excellent reproduction of ignition timing even when EGR is employed.

To enable non-throttling operation of gasoline S.I. engine, we have manufactured engines equipped with a newly developed Hydraulic Variable-valve Train (HVT), which can vary its intake-valve closing-timing freely. The air-intake control ability of HVT engine is equivalent to conventional throttling engines. Combustion becomes unstable, however, under non-throttling operation at idling. For the countermeasure, newly designed combustion chamber has been developed. The reduction of pumping loss by the HVT depends on engine speed rather than load, and amounts to about 80 % maximum. A conventional engine-management system is not applicable for non-throttling operation. Therefore, new management system has been developed for load control.